On average, listings lease in the $30's per square foot per year. The Downtown Chicago submarket is going through a a boost in rates. In the last 3 months, the median rate rose $1 per sqft per year. That's a 2% increase in rent.
Compared to the rest of the Chicagoland market, the Downtown Chicago submarket has greater rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 371 listings have been listed, so you'll want to check back regularly for new listings. About 5% of the available space in the Downtown Chicago are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
Even though the median size is 2,810 sqft, there are still 0 new availabilities below 2,000 sqft. Most properties in this area are around 12 floors. Most buildings in this market were built in 1929 and are Class B.